In recent years, various electrical devices have been equipped with backup power supplies to prevent problems arising from a failure of the main power supply. For example, some modern time recorders use an AC power line as their main power supply. When the AC power line fails, the power supply is switched to the backup power supply to back up the stored data, the clock, and so on. These devices have a manual switch connected between the backup power supply and the load. When the device is shipped from the factory, this switch is operated to disconnect the backup power supply from the load, thus preventing wasteful consumption of the backup power supply. When the device is used, the switch is again operated to operatively connect the backup power supply to the load so that backup is enabled.
When using the above-described prior art device, the user often forgets to operate the switch of this device. In this case, the equipment is used while the backup power supply remains operatively disconnected therefrom. As a result, in the case of a failure of the main power supply, a fatal situation can arise since the electrical device is not backed up.